Conventionally, the linear bushing is composed of an elongated shaft and a slider which fits over the shaft to move along the shaft. The slider has an outer cylinder and a ball retainer made of synthetic resins and so on and installed in the outer cylinder to retain rolling elements therein. Moreover, the ball retainer is held in the outer cylinder with retainer rings which fit in grooves made at opposite ends of the outer cylinder, lest it falls off from the outer cylinder.
With the polygonal ball bushing disclosed in Japanese Laid-Open Patent Application No. S50-70 759, plane or flat surfaces are combined with curved surfaces in such a relation that apices around the polygon are inscribed with a circular surface of the housing.
One of prior ball bushings disclosed in for example Japanese Publication No. S59-11 771, which comprises a lengthwise outer sleeve with raceways formed therein, and having an axial bore and a retainer including a plurality of ball guideways distributed over the periphery thereof. The ball guideways comprise guideway sections and semicircular turnaround passages connecting the ball guideways by pairs. The balls are arranged in the ball guideways to roll through there in an endless manner. The outer sleeve having the lengthwise raceways and return passages has a length which substantially corresponds to the length of the axial guideway sections in the retainer, the retainer being made of synthetic material and projecting with the semicircular deflecting way sections beyond the outer sleeve, and end rings mounted on projecting sections of the retainer for covering the deflecting zone.
With the polygonal ball bushing constructed as stated earlier, there has been troublesome issue on assembling process. More especially, as the conventional linear bushing needs the end rings for fastening the outer sleeve of the retainer, the end rings fit into grooves which have been cut at opposite ends of an inside circular surface of the outer sleeve. The assembling procedure as stated just earlier requires many parts and components and, therefore, can lead to problems that part and components are increased in number and sophisticated in construction. With the prior ball bushings, moreover, the outer sleeve is covered with plastic-made end rings at the opposite ends projecting beyond opposite ends of the outer sleeve. Because the projecting sections around the inside circular surfaces of the end rings should be swaged against the ends of the retainer, the assembling procedure needs troublesome chores. Cuts made in the sleeve of the retainer causes the restrictions on the insert direction of the end rings into the retainer.
In the commonly assigned Japanese senior Laid-Open Patent Application No. 2015-45 365, there is disclosed a linear ball bushing in which the outer sleeve and the retainer are made in one-piece construction to reduce parts and components in number and further the retainer is placed accurately relative to the outer sleeve and fastened firmly to the outer sleeve. With the linear ball bushing constructed as stated just earlier, the retainer has at least one pair of protections projecting out of the opposite ends of the outside surface of the retainer and outer sleeve has windows extending in lengthwise direction to fit over the pair of projections. After the pair of projections has fit into the windows in the outer sleeve, the retainer is kept in place against both rotation and lengthwise movement. With the linear ball bushing constructed as stated earlier, however, as the outer sleeve has the window to expose outside the circulating circuit for the balls, there is a fear or problem that any foreign materials of dust and dirt would invade into the circulating circuit for the balls.